For a correction of ametropia, e.g. by laser surgery of the cornea, a variety of instruments are required, the design of which is appropriate to the respective purpose. At the beginning of such a treatment, instruments are used that are suitable for eye diagnosis, such as, for example, surgical microscopes, optical arrangements for 3D measurement on the cornea, or arrangements for optical coherence tomography. Depending on the result of the diagnosis, therapeutic measures are then settled on and carried out.
Before one can start the actual correction of ametropia by the removal of tissue off the cornea, one must, in the method known as LASIK, first produce a lid on the surface of the cornea that can be folded up and is known as a flap, the thickness of which is substantially less than the thickness of the cornea itself. For this purpose, a “flap-cutting” laser instrument is used, which is known in prior art as a laser keratome or microkeratome. This instrument is used to produce a succession of many photodisruptions of the tissue, each measuring a few micrometers only, which together constitute the flap; this process requires highly precise positioning of the laser beam focus within the cornea in both lateral and axial direction. The treatment laser beam used for this has pulse widths of less than 10−12 s.
By application of another optical precision instrument and with the flap folded away to expose the internal tissue region, then, tissue is removed off that exposed region to vary the curvature of the cornea until the ametropia is corrected. The removal of tissue is accomplished, e.g., by energy input with a pulsed treatment laser beam. The instruments designed for removing the tissue are known as laser ablation instruments. Alternatively, a method can be employed that is exclusively carried out with a femtosecond laser therapy instrument. Modern methods of lenticular extraction are known by the names of FLEx and SMILE; methods also possible are radial keratotomy (RK) or annular cuts.
The result of the treatment is assessed with a diagnostic instrument, e.g., a 3D measuring instrument, in order to carry out subsequent corrective treatments, if necessary.
All instruments employed have to be positioned relative to the eye according to their respective tasks; they all need to occupy the same working or treatment area surrounding the eye, from which it follows that this area has to be occupied and cleared by each instrument in succession. For an efficient process sequence, the instruments for the successive process steps should be available in the immediate vicinity without, however, obstructing each other by blocking the working or treatment area. Moreover, it should be avoided, if possible, that the patient's eye to be treated has to be re-aligned after each instrument change as required for therapy or diagnosis.
An added requirement is that, at least temporarily, free space for manual operations on the eye must be available; typically, such operations are observed through a surgical microscope. Often, an instrument for ultrasonic phacoemulsification must be kept available in addition, since a complete emulsification of the crystalline lens by application of femtosecond laser is not possible with cataracts of the 2nd to 4th degrees. In these cases, an ultrasonic phacoemulsification instrument must be employed as a complement to laser treatment, in order to complete the fragmentation of the crystalline lens. Subsequently, the phacoemulsification instrument must be switched to the irrigation/aspiration mode for removing the lens residues and the cortex from the capsule. For these instruments, too, the treatment area has to be cleared, if necessary.
For the efficiency of the treatment process, patient positioning and patient transport are relevant as well. With the refractive surgery described above, what are important apart from maximum position accuracy are comfort as well as aesthetic aspects, whereas the requirements in case of a cataract operation differ in so far as the patients have to be safely positioned in a locally or generally anaesthetized state.
An aspect of particular importance and not to be ignored in the treatment and therapy of the human eye and especially in case of surgical intervention is the sterility of the laser instrument, particularly those objects and parts of the laser instrument that get into contact with the hands of the surgeon and the assistants. Sterilizing the entire laser instrument, though, is extremely difficult and, in fact, impracticable.